title: A Klothoβ variant mediates protein stability and associates with colon transit in irritable bowel syndrome with diarrhea.
abstract: OBJECTIVE
  Bile acid (BA) malabsorption of moderate severity is reported in 32% of patients with chronic unexplained diarrhea, including diarrhea-predominant irritable bowel syndrome (IBS-D). We hypothesized that variants of genes regulating hepatic BA synthesis play a role in IBS-D.
  
  
  METHODS
  In 435 IBS and 279 healthy subjects, we tested individual associations of 15 common single nucleotide polymorphisms (SNPs) from 7 genes critical to BA homeostasis with symptom-based subgroups using dominant genetic models. In a subset of 238 participants, we tested association with colonic transit. SNP-SNP interactions were investigated based on known protein interactions in BA homeostasis. The function of SNP rs17618244 in Klothoβ (KLB) was evaluated using a protein stability assay in HEK293 cells.
  
  
  RESULTS
  SNP rs17618244 (Arg728Gln in KLB) is associated with colonic transit at 24 hours. G allele (Arg728) compared with A allele (Gln728) is associated with accelerated colonic transit (P=.0007) in the overall cohort; this association was restricted to IBS-D (P=.0018). Interaction tests of KLB rs17618244 with 3 nonsynonymous SNPs of fibroblast growth factor receptor 4 (FGFR4) revealed that rs1966265 (Val10Ile) and rs351855 (Gly388Arg) modulate rs1768244's association with colonic transit in IBS-D (P=.0025 and P=.0023, respectively). KLB Arg728 significantly reduced protein stability compared with KLB Gln728, demonstrating KLB rs17618244's functional significance. No significant associations with symptom-based subgroups of IBS were detected.
  
  
  CONCLUSIONS
  A functional KLB gene variant mediating protein stability associates with colonic transit in IBS-D. This association is modulated by 2 genetic variants in FGFR4. The FGF19-FGFR4-KLB pathway links regulation of BA synthesis to colonic transit in IBS-D.
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Health Sciences Research, College of Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: Banny S
authors.initials: BS
authors.lastname: Wong
authors.forename: Michael
authors.initials: M
authors.lastname: Camilleri
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Carlson
authors.forename: Maria E
authors.initials: ME
authors.lastname: Guicciardi
authors.forename: Duane
authors.initials: D
authors.lastname: Burton
authors.forename: Sanna
authors.initials: S
authors.lastname: McKinzie
authors.forename: Archana S
authors.initials: AS
authors.lastname: Rao
authors.forename: Alan R
authors.initials: AR
authors.lastname: Zinsmeister
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Gores
mesh_terms: D000328:Adult; D001647:Bile Acids and Salts / Q000378:metabolism; D016022:Case-Control Studies; D003106:Colon / Q000378:metabolism / Q000503:physiopathology*; D003967:Diarrhea / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D005260:Female; D005769:Gastrointestinal Motility / Q000235:genetics; D005787:Gene Frequency; D056726:Genetic Association Studies; D020022:Genetic Predisposition to Disease; D057809:HEK293 Cells; D006801:Humans; D043183:Irritable Bowel Syndrome / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D007700:Kinetics; D000090265:Klotho Proteins; D008099:Liver / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D008875:Middle Aged; D008910:Minnesota; D008957:Models, Genetic; D015233:Models, Statistical; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D055550:Protein Stability; D051499:Receptor, Fibroblast Growth Factor, Type 4 / Q000235:genetics; D014162:Transfection
chemical_list: D001647:Bile Acids and Salts; C538995:KLB protein, human; D008565:Membrane Proteins; C496371:FGFR4 protein, human; D051499:Receptor, Fibroblast Growth Factor, Type 4; D000090265:Klotho Proteins